This invention relates to a method of making an industrial mineral filler from fly ash, and more particularly, it relates to a method in which raw fly ash is dry processed into fine fractions which can be utilized as a filler product.
Fly ash is a by-product derived from the combustion of coal and comprises finely divided inorganic products. Enormous amounts of fly ash are produced annually nationwide, primarily from burning coal in electric power plants. Disposal of fly ash has posed an increasingly difficult problem because the volume, the particulate nature, and the varied chemical composition of fly ash limit the number of acceptable disposal sites.
Accordingly, efforts have been made to find alternative, economic uses for fly ash. For example, fly ash has been used as an additive in portland cement. However, the fraction of fly ash which is suitable for use in concrete represents only a small portion of the total fly ash available. It would be desirable to find other uses for the fly ash material.
One such potential use for fly ash is as an industrial mineral filler. Mineral fillers are widely used in plastic products to improve performance and reduce costs. Mineral fillers commonly used for applications such as plastics, compounding, injection molding, paper products and the like include calcium carbonate, kaolin, aluminum hydrate, mica, talc and ground silica. Titanium oxide is also currently in wide use as a commercial filler, but is very expensive. The chemistry and characteristics of fly ash are close to those of such commercial fillers and would be a desirable substitute. However, the particle size of fly ash is much larger than that of typical commercial fillers. Wet processing such as wet milling, froth flotation, attrition grinding, and wet magnetic iron removal have been used in the past to reduce and control the particle size of fly ash. However, such methods are complicated, expensive, and require a multi-step process as the wet fly ash must be oven dried. In addition, methods such as froth flotation utilize reagents such as turpentine which must be safely disposed of.
Accordingly, there is still a need in the art for a method of producing mineral filler from fly ash which is economical, easy to implement, and which produces a usable particle size distribution.